In the design of the mixed-signal integrated circuits, minimization of chip surface area and noise optimization are typically two critical goals. One technique, which generally addresses both problems, is the utilization of low voltage transistors, operating from a low voltage supply rail, in at least some parts of the circuitry. Low voltage field effect transistors have shorter channel lengths and thus consume less chip surface area. Low voltage transistors also normally generate less noise and the associated lower gate voltage swing typically results in reduced total harmonic distortion in the output signal.
The utilization of low voltage transistors in conjunction with other on-chip devices and circuits operating at higher voltages dictates the use of intervening voltage level shifters. Level shifting circuitry, however, can further increase the overall level of noise in the system. Therefore, level shifting circuits and methods are required which provide the required level of voltage shifting, yet introduce a minimal level of additional system noise.